Frequency-control system



Dec. 11, 1923. 1,476,721

oa hgoss K. MARTIN FREQiIENCY CONTROL SYSTEM Filed Nov. 23 1921 INVENTORWQ ATTORNEY Patented Dec. 11, 1923.

UNITED STATES PATENT OFFICE.

. DE LOSS K. MARTIN, OF ORANGE, NEW JERSEY, ASSIGNOR TO AMERICANTELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

FREQUENCY-CONTROL SYSTEM.

Application filed November 23, 1921. Serial No. 517,335.

To all whom it may concern:

Be it known that I, DE Loss K. MARTIN, residing at Orange, in the countyof Essex and State of New Jersey, have invented certain Improvements inFrequency-Control Systems, of which the following is a specification.

This invention relates to signalling by means of carrier frequencies andmore particularly to an arrangement for controlling the carrierfrequency used for signaling by different stations. I In a system,either wire or radio, employing carrier currents for transmissionpurposes, it is frequently desirable that some method be available forcontrolling the cartween stations of different systems.

rier frequency at one station from a distant station. In a wire carriersystem, for example, it is necessary, where the homodyne method ofreceiving is employed, to properly synchronize the frequencies used forreceiving with the frequencies used for transmitting at the distantstation. and it is also desirablethat the spacingof the carrierfrequencies employed by the various channels be maintained in the samerelation. In a radio system the same situation arises, and in additionit is desirable that the frequencies assigned to different stations andto groups of stations belonging to different systems be maintained inproper spacial relation. This is necessary in the one case to preventinterference, between different signaling stations of the same systemand in the other case to prevent interference bIen either case it isdesirable to transmit from some controlling station a master frequencyand to provide at each signaling station arrangements whereby thecarrier frequencies employed may be determined by the master frequency.

All of these situations call for some arrangement whereby a frequencyatone station may be controlled from a distant station. In accordance withthe present invention it is proposed to accomplish this result byarranging the circuits of a vacuum tube oscillator, so that theparticular frequency at which the vacuum tube will oscillate willcorrespond either to the master frequency or to a frequency derivedtherefrom. The principle .here employed is analo us to the well-knownhenomena observe in connection with a ternating current generators,namely, that when two alternators are connected into the same 'cir-'cuit and are rotated at substantially the same frequency, bothalternators tend to rotate in synchronism, and, as soon as synchronismhas been reached, this condition will continue indefinitely.

The invention may now be more fully understood from the followingdescription when read in connection with the accompanying drawing,Figures 1 and 2 of which show schematically two arrangements embodyingthe principles of the invention.

Referring to Fig. 1, O is a vacuum tube oscillator having the usualfilament, grid and plate. The tuned grid circuit 10 is coupled to theplate circuit 11 and to the outgoing circuit 12 through the windings ofa transformer 13, this arrangement providing a feed-back arrangementbetween the grid circuit and the plate circuit. By means of someadjustable element, such, for example, as the condenser 14, the circuitsof the oscillator may be tuned so that it will oscillate at a givenfrequency. If, however, another frequency not greatly different from thenatural frequency of the system be impressed upon the plate circuit, thetube will oscillate at the frequency impressed on the plate circuitrather than at its own natural frequency, provided, of course, that thearrangement which generates the frequency impressed upon the platecircuit is so related to the oscillator that the oscillator does notreact upon such generator.

This condition is'realized in a radio system, such as that shown in Fig.1 for example. In this system the receiving antenna RA will receive amaster controlling frequency, for example, and a filter F is associatedwith the antenna to render the circuit selective to the controlfrequency. Thi filter may be either a simple tuned circuit of well knowntype or a band filter of the Campbell type. If desired, an amplifier Amay be provided to amplify the master frequency to any desired valuebefore impressing it upon the oscillator. The amplified master frequencymay be impressed upon the plate circuit of the oscillator through atransformer 15 in the output circuit of the amplifier A, it beingunderstood that the amplifier A may be of any well-known type, such, forexample, as a vacuum tube.

In the case of a circuit such as that desynchronism with the-frequencygig I emma scribed the master frequency generated at a distant pointwill be wholly inde ndent of the frequency of the oscillator owing tothe fact that the master frequency is radiated from a distant point andreceived by the antenna RA, and the frequency generated by theoscillator cannot be transmitted back to the generator ofthe master freuency. Consequently, by reason of the wel -known principle that twooscillators approachin the same frequency and connected to t e samecircuit tend to oscillate at the same frequency, it at once follows thatthe oscillator 0 will oscillate at the master frequency, assuming, ofcourse, that the master frequency does not greatly differ from thatwhich would normally be generated by the oscillator O.

This it will be seen affords a simple arrangement forkeeping theoscillations enerated by the vacuum tube oscillator in enerated at adistant oint. The same resu t may be accomplishe by the arrangementshown in Fig. 2, which difiers from that of Fi 1 in that the masterfrequency is impresse upon the id circuit of the vacuum tube 0 instea ofupon the plate circuit. The grid and plate circuits are coupled togetherthrough the transformer 13, and the frequency generated is impressedupon the work circuit 12 through a transformer 13 in the plate circuit.The rid circuit is connected thro h the trans ormer 15 with theamplifier filter F and receiving antenna RA, so that the masterfrequency ma be transmitted to the tube for contro ling purposes. Theoperation will, of course, be similar to that of Fig. 1 and need not befurther described.

It will be obvious that the general principles herein disclosed may beemployed in man other organizations widely different om thoseillustrated without deartin from the spirit of the invention as efine inthe following claims.

What is claimed is:

1. The method'of producing synchronism.

device, and in impressing t e controlling to frequency thus passed uponthe oscillator whereby the oscillator will oscillate 1n synchronism withthe controlling frequency.

2. The method of producing synchronism between a locally generatedfrequency and a controlling frequency transmitted from a distant oint,which consists in adjusting an oscil ator to oscillate at a fre uency inthe neighborhood of the contro 'ng fre- (f uency, radiating thecontrolling frequency rom a distance point, receiving trolling frequencyat the generatm station, transmitting the controlling requency through aone-way device, and impressing the controlling frequency thus passedupon the oscillator whereby the oscillator will oscillate in synchronismwith the controlling frequency.

3 A system for producing synchronism between a locally generatedfrequency and a controlling frequency transmitted from a distant pointcomprising an oscillator ad justed to oscillate at a frequency in theneighborhood of the controlling frequency, means to receive thecontrolling fre uency, a one-way device through which t e receivedcontrolling frequency may be transmitted, and means to im ress thecontrolling frequency so transmitted upon the oscillator whereby it willoscillate at the controlling frequency. 7

4:. A system for producing synchronism between a locally generated freuency and a controlling frequency generate from a distant pointcomprisin a vacuum tube oscillator adjusted to oscl late at a fr uencyin the neighborhood of the control ing frequency, means to receive thecontrolling frequency, a one-wa device through which the received controing frequency may be transmit, and means to impress the controllingfrequency so transmitted upon the circuit of the vacuum tube oscillatorwhereby jthe oscillator will oscillate at the con ice DE SS K.

the con-

